Electron discharge device



Feb. 3,- 1942. G. A. MoRfroN 2,271,985

ELECTRON DISCHARGE DEVICE Filed Sept. l, 1959- Iggy.

1////// lll/X719 Buncntor xttorneg Patented Feb. 3, 1942 ELECTRON DISCHARGE DEVICE George Ashmun Morton, Haddon Heights, N. J., assignor to` Radio Corporation of America, a

corporation of Delaware 7 Claims.

This invention relates to electron discharge devices and to methods of operating the same and has for its principal object to provide an electron tube the operation of which is characterized by a high ratio of transconductance to current.

It is known to those skilled in the art to which this invention appertains that if electrons can be made to approach the control grid of an ampliiier device with a minimum range of velocities (instead of with the Maxwellian velocity distribution which obtains adjacent their area of origin) then a very small grid swing is suioient to control the electron current from saturation to cut-oli. To this end it has previously been proposed (see Zworykin et al. 2,157,585) to provide a pair of collimating plates mounted intermediate the cathode and grid and an external magnet, so that, under the opposing forces of the electrostatic and magnetic ields, the electrons within a certain velocity range are caused to pass through the collimating electrodes and approach the grid while the electrons having other velocities and velocity components will be drawn to one or the other of these plates and effectively lost. While discharge devices employing such electron velocity filters exhibit a high value of transconductance to current (which is manifest in the steepness of its Egp characteristic curve) as compared to the usual grid controlled tube, it may be said generally that the magnet renders the device cumbersome and, further, may introduce disturbing electrical eliects in the associated circuits and apparatus.

Accordingly another and important object of the present invention is to provide a grid controlled electron discharge tube incorporating a simplified ltering device which is operable without the use of an auxiliary magnet.

The above and `other objects are achieved in accordance with the invention by making use of the velocity lter properties of an electrostatically actuated electron mirror.

Certain details of construction together with other objects and advantages will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawing, wherein:

Figure 1 is a longitudinal sectional View oi a three element electron mirror which will be referred to in explaining the principle of the invention,

Figures 2, 3 and 4 are curves illustrative of the electron filtering action of the device of Fig. l, and

Figure 5 is a sectional View of a grid controlled electron multiplier device incorporating an electron mirror which is constructed and arranged in accordance with the principle o the invention.

As above indicated the present invention is predicated upon an appreciation of the fact that it is possible to design an electron mirror which will allow all electrons above a specied velocity to pass through it while reiiecting back all electrons having lower velocities. Such an electron mirror is shown in Fig. 1 in the form of three cylinders, I, 2 and 3, respectively, which are arranged in spaced relation along a common axis. When the terminal cylinders l and 3 are each maintained at a potential higher than that of the central cylinder 2 an electrostatic iield having equipotential surfaces similar to those indicated by the dotted lines will be generated. If, now, a family of electrons A (Figs. l and 2), whose initial velocities embrace a range of from zero to, say, three-tenths of a volt, enters the rst cylinder then the electrons whose initial velocity was zero will reach the zero potential surface and will be reflected in the return direction, since at that point they lose all of the velocity which they acquired in approaching the rst positively charged cylinder l. Similarly, those electrons whose initial velocities were from zero to, say, .1 or .2 volt (depending on the exact potential distribution among the cylinders) and which are designated B in both Figs. l and 3, will reach equal potential surfaces of the same relative value and be caused to leave the cylinder l in the return direction. On the other hand. the electrons C (Figs. 1 and 4) which have a higher initial velocity sufficient to bring them within the influence of the eld adjacent the third cylinder, will not be reflected but will continue in their original direction of travel until they impinge a collecting surface, such, for example, as the closed end 3a of that cylinder. Thus the device of Fig. 1 may be said to have a dual function, i. e., it serves as an electron mirror for the low velocity electrons B and as an electron lens for passing and focusing the higher velocity electrons C to and upon the collecting surface 3a.

Assuming now that the potential distribution among the cylinders l, 2 and 3 of Fig. l is such that the electrons leaving the cylinder l in the return direction have a velocity range of from 0 to .1 of a volt and assuming further that these electrons can be subject to a control potential, then the variation in such control potential required to control these electrons from cut-off to saturation need be only one-tenth of a volt. It follows that a device incorporating these features will, in operation, exhibit an extremely high ratio of transconductance to current and will possess a useful sensitivity far greater than that of the usual grid controlled amplifier or other discharge tube.

As previously set forth and as indicated in Figs. 3 and 4, a considerable percentage of the Y neck portion Illa.

electrons entering the rst mirror cylinder pass directly to the collecting surface 3a (Fig. 1), where they are effectively lost, so that only a part (i. e., the reflected electrons) of the original electron stream will ordinarily be usefully employed. Thus, unless some :means is provided to compensate for this loss, the power output will be less than that of an ordinary tube of similar dimensions. To compensate for this loss, one or more electron multiplier stages may be provided intermediate the control stage and the output electrode.

Fig. 5 shows the invention as embodied in an electron multiplier of the electrostatic type disclosed in copending application to Rajchman and Pike, Serial No. 171,916, iiled October 30, 1937 (now U. S. Patent 2,231,682, issued February 11, 1941). In Fig. 5 there is shown an evacuated tube having a body portion I and dependent Mounted at the knee of the tube to one side of the central axis of the dependent neck Illa is a thermionic cathode 4I partially surrounded by a shield 5 which has an exit aperture 5a directed downwardly toward the open .end of the electron mirror elements I, 2 and 3. On the other side of the common axis of the mirror elements adjacent the open end of the mirror, there is a grid-like electrode 6 which spansthe aperture of a small cylinder 'I through which the electrons, which are reflected from the mirror, enter the body section I0 of the tube. The electron multiplier device which is mounted in the body section of the tube comprises two sets (i. e., upper and 1ower) of substantially L- shape multiplying electrodes II to I1, inclusive, g

mounted in staggered relation on opposite sides of a median line which extends from the electrode II through the electron path to the Output electrode or anode I8.

In operating the device of Fig. 5, the cathode shield 5 and the apertured electrode 'I should ordinarily be maintained at approximately the same potential, say, three volts positive with respect to the cath-ode. Similarly, the first (I) and the last (3) of the mirror cylinders may be main- A tained at a potential a few Volts, say two volts, positive with respect to the cathode, in which case the middle cylinder 2 should be adjusted to a potential which is slightly (say 0.1 volt) negative with respect to the cathode. The multiplying stages may be operated in the usual manner, that is to say, the potential applied to each of the electrodes II to I8, inclusive, should be higher than that of the next preceding electrode. Thus, if the potential applied to electrode II is 100 volts positive with respect to the cathode, then the potential applied to electrode I2 may be 200 volts and that applied to the electrode I3y 300 volts, and so on for as many stages as desired.

With the device of Fig. 5 energized in the manner above described, the path of the high velocity electrons extends along the path C from the cathode 4 through the mirror to the closure 3a on the last mirror cylinder where they are effectively llost. The path of the low velocity electrons which are reflected from the mirror is indicated by the dotted une B.

lInsome cases, as where the device is to be employed as an audio amplifier, the grid electrode may be dispensed with and the mirror itself used as the control element. In this case, the

controlling Voltage is preferably applied to the central mirror electrode 2.

Other modications of the invention, such, for example, as the substitution of flat or of bent plates for the cylindrical mirror elementshere illustrated, and the substitution of another type of electron multiplier, will suggest themselves to those skilled in the art. It is to be understood, therefore, that the foregoing description of a preferred embodiment -of the invention is to be interpreted as illustrative and not in a limiting sense, except as required by the prior art and by the spirit of the appended claims.

What is claimed is:

1. Method of operating an electron discharge device which comprises generating a stream of electrons having various velocities, generating an electrostatic eld comprising equipotential surfaces adapted to reflect electrons of certain of said velocities and to pass the electrons of other velocities, directing said electron stream toward said electrostatic eld, separately collecting the reflected and the passed of `said electrons and subjecting the reected electrons to a controlling potential prior to their collection.

2. Method of operating an electron discharge device which comprises generating a stream of electrons having various velocities, generating an electrostatic eld capable of reflecting back, in the direction of their origin, the electrons of lower velocities and to pass the higher velocity electrons, directing said electron stream upon said electrostatic field, collecting the passed electrons, subjecting the reected electrons to a control potential and then collecting said reected electrons.

3. An electron discharge device comprising a cathode adapted to release electrons having various velocities, an electron mirror accessible to all of said electrons, said mirror being adapted to reflect electrons having certain velocities and to pass electrons having other velocities, and a control electrode mounted in the path of said reflected electrons.

4, An electron discharge device comprising a cathode adapted to release electrons having various velocities, an electron mirror accessible to all of said electrons, said mirror being adapted to reflect electrons having certain velocities and to pass electrons having other velocities, a control electrode mounted in the path of said reflected electrons and an electrode surface upon which said other electrons impinge.

5. An electron discharge device comprising a cathode adapted to release electrons having various velocities, an electron mirror comprising a plurality of electrodes mounted in spaced relation in the path of said electrons and provided with electrode leads for establishing an electrostatic eld among said electrodes capable of reflecting back, in the direction of their origin, the electrons of lower velocities and of passing the higher velocity electrons, an electron multiplying electrode and means for directing said reilected electrons to said multiplying electrode.

6. The invention as set forth in claim 5 and wherein a control grid is mounted in the path of said reflected electrons.

7. The invention as set forth in claim 5 and wherein one of said mirror electrodes comprises a control electrode.

GEORGE ASHMUN MORTON. 

